Concentrating solar power with glasshouses

ABSTRACT

A protective transparent enclosure, such as a greenhouse, encloses a concentrated solar power system having line-focus solar energy concentrators. The line-focus solar energy concentrators have a reflective front layer, a core layer, and a rear layer. The core and the rear layers, when bonded with the reflective front layer, enable the line-focus solar energy concentrator, in some embodiments, to retain a particular form without additional strengthening elements. In some embodiments, the core layer and/or the rear layer are formed by removing material from a single piece of material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT/US2012/025832 filed Feb. 20,2012 entitled “CONCENTRATING SOLAR POWER WITH GLASSHOUSES”, which claimsbenefit of priority to U.S. Provisional Application No. 61/445,518,filed Feb. 22, 2011 entitled “CONCENTRATING SOLAR POWER WITHGLASSHOUSES. To the extent permitted by the type of the instantapplication, this application incorporates by reference for all purposesthe following applications, all commonly owned with the instantapplication at the time the invention was made:

-   -   PCT Application (Serial No. PCT/US10/22780), filed Feb. 1, 2010,        first named inventor Roderick MacGregor, and entitled        Concentrating Solar Power with Glasshouses;    -   U.S. Provisional Application Ser. No. 61/361,509, filed Jul. 5,        2010, first named inventor Peter Von Behrens, and entitled        Concentrating Solar Power with Glasshouses; and    -   U.S. Provisional Application Ser. No. 61/445,518, filed Feb. 22,        2011, first named inventor Peter Von Behrens, and entitled        Concentrating Solar Power with Glasshouses.

BACKGROUND

1. Field

Advancements in concentrated solar thermal power (CST), photovoltaicsolar energy (PV), concentrated photovoltaic solar energy (CPV), andindustrial use of concentrated solar thermal energy are needed toprovide improvements in performance, efficiency, and utility of use.

2. Related Art

Unless expressly identified as being publicly or well known, mentionherein of techniques and concepts, including for context, definitions,or comparison purposes, should not be construed as an admission thatsuch techniques and concepts are previously publicly known or otherwisepart of the prior art. All references cited herein (if any), includingpatents, patent applications, and publications, are hereby incorporatedby reference in their entireties, whether specifically incorporated ornot, for all purposes.

Concentrated solar power systems use mirrors, known as concentrators, togather solar energy over a large space and aim and focus the energy atreceivers that convert incoming solar energy to another form, such asheat or electricity. There are several advantages, in some usagescenarios, to concentrated systems over simpler systems that directlyuse incident solar energy. One advantage is that more concentrated solarenergy is more efficiently transformed to heat or electricity than lessconcentrated solar energy. Thermal and photovoltaic solar receiversoperate more efficiently at higher incident solar energy levels. Anotheradvantage is that non-concentrated solar energy receivers are, in someusage scenarios, more expensive than mirror systems used to concentratesunlight. Thus, by building a system with mirrors, total cost ofgathering sunlight over a given area and converting the gatheredsunlight to useful energy is reduced.

A line-focus receiver is a receiver with a target that is a relativelylong straight line, like a pipe. A line-focus concentrator is areflector (made up of a single smooth reflective surface, multiple fixedfacets, or multiple movable Fresnel facets) that receives sunlight overa two dimensional space and concentrates the sunlight into asignificantly smaller focal point in one dimension (width) whilereflecting the sunlight without concentration in the other dimension(length) thus creating a focal line. A line-focus concentrator with aline-focus receiver at its focal line is a basic trough system. Theconcentrator is optionally rotated in one dimension around its focalline to track daily or seasonal (apparent) movement of the sun toimprove total energy capture and conversion.

A parabolic trough system is a line concentrating system using amonolithic reflector shaped like a large half pipe having a shapedefined by the equation y²=4 fx where f is the focal length of thetrough. The reflector has a 1-dimensional curvature to focus sunlightonto a line-focus receiver or approximates such curvature throughmultiple facets fixed relative to each other.

A concentrating Fresnel reflector is a line concentrating system similarto the parabolic trough replacing the trough with a series of mirrors,each the length of a receiver, that are flat or alternatively slightlycurved in width. Each mirror is individually rotated about its long axisto aim incident sunlight onto the line-focus receiver.

In some concentrated solar systems, such as some systems with highconcentration ratios, overall system is cost dominated by variouselements such as the concentration system (such as a mirror or lens), asupport system for the concentrators, and motors and mechanisms thatenable tracking movement of the sun. The elements dominate the costsbecause the elements are enabled to withstand wind and weather. In someusage scenarios, solar energy systems are enabled to withstand variousenvironmental dangers such as wind, rain, snow, ice, hail, dew, rodents,birds and other animals, dust, sand, moss, and other living organisms.Reflectivity of a concentrator is sensitive to damage, tarnishing, anddirt buildup since only directly reflected sunlight, not scatteredsunlight, is effectively focused.

Glass mirrors are used in some concentrated systems, because of anability to maintain good optical properties over long design lives (e.g.30 years) of concentrated solar systems. Glass is relatively fragile andvulnerable to hail and other forms of damage unless it is suitablythick, e.g. 4-5 mm for relatively larger mirrors. In a 400 square footconcentrating dish the thickness results in a weight of close to 1000lbs or about nine kg per square meter of concentrator area. The mirroris formed in a precise curve, in one dimension for a trough, in twodimensions for a dish, to focus sunlight.

In some concentrated systems, mirror surfaces cease to focus as intendedif warped. Thus, the reflector is supported and held in shape by a metalsuperstructure that is shaped to the curved glass. The superstructuresupports and protects the mirror from environmental conditions such aswinds of 75 mph or more. The protection from winds adds an additional10,000 lbs of load beyond the 1000 lb weight of the mirror, resulting incomplex construction requiring roughly 20 kg of structural steel forevery square meter of mirror area in a dish system.

SYNOPSIS

The invention may be implemented in numerous ways, including as aprocess, an article of manufacture, an apparatus, a system, and acomposition of matter. In this specification, these implementations, orany other form that the invention may take, may be referred to astechniques. The Detailed Description provides an exposition of one ormore embodiments of the invention that enable improvements inperformance, efficiency, and utility of use in the field identifiedabove. The Detailed Description includes an introduction to facilitatethe more rapid understanding of the remainder of the DetailedDescription. As is discussed in more detail in the Conclusions, theinvention encompasses all possible modifications and variations withinthe scope of the issued claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a perspective view of selected details of a portionof an embodiment of an enclosing greenhouse and an enclosed concentratedsolar energy system utilizing a parabolic trough with a unilateralextension.

FIG. 2 illustrates a cross-section view of a bilaterally symmetrictrough with a symmetric portion and a unilateral extension collectivelyhaving one continuous shape.

FIG. 3 illustrates a perspective view of selected details of anembodiment of a parabolic trough solar concentrator with a unilateralextension, a solar receiver, and a suspension mechanism that enable thesolar concentrator to rotate about the solar receiver.

FIG. 4 illustrates in exploded perspective view a section of a sandwichstructured composite with a honeycomb core.

FIG. 5a illustrates, in plan view, an embodiment of mirror constructionvia a sandwich structured composite having two skins and one core, withno material removed. Each layer is illustrated separately, not asstacked during construction.

FIG. 5b illustrates, in exploded section view referenced to Section line66 in FIG. 5a , an embodiment of mirror construction via a sandwichstructured composite having two skins and one core, with no materialremoved.

FIG. 6a illustrates, in plan view, an embodiment of mirror constructionvia a sandwich structured composite having two skins (front and rear)and one core, with sections removed from the core and the rear skin.Each layer is illustrated separately, not as stacked duringconstruction.

FIGS. 6b and 6c respectively illustrate exploded section viewsreferenced, respectively, to Section lines 1 72 and 2 73 of FIG. 6 a.

FIG. 7a illustrates, in plan view, an embodiment of mirror constructionvia a sandwich structured composite having two skins (front and rear)and one core, with the core and the rear skin sections built from stripsof material. Each layer is illustrated separately, not as stacked duringconstruction.

FIGS. 7b and 7c respectively illustrate exploded section viewsreferenced, respectively, to Section lines 1 77 and 2 78 of FIG. 7 a.

FIG. 8a illustrates, in plan view, an embodiment of mirror constructionvia a sandwich structured composite having three skins (front, middle,and rear) and two cores (front and rear), with sections removed from therear core and the rear skin. Each layer is illustrated separately, notas stacked during construction.

FIGS. 8b and 8c illustrate exploded section views referenced,respectively, to Section lines 1 87 and 2 88 of FIG. 8 a.

FIG. 9a illustrates, in plan view, an embodiment of mirror constructionvia a sandwich structured composite having three skins (front, middle,and rear) and two cores (front and rear), with the rear core and therear skin sections built from strips of material. Each layer isillustrated separately, not as stacked during construction.

FIGS. 9b and 9c illustrate exploded section views referenced,respectively, to Section lines 1 97 and 2 98 of FIG. 9 a.

FIG. 10 illustrates, in plan view as seen from the non-reflective (e.g.back) side of the mirror, an embodiment of mirror construction via asandwich structured composite having multiple pre-formed mirrorsegments, each segment implementing a full aperture of a mirror shape asjoined by flanges.

FIG. 11 illustrates, in plan view as seen from the back side of mirror,another embodiment of mirror construction via a sandwich structuredcomposite having multiple pre-formed mirror segments, each segmentimplementing a portion of a full aperture of a mirror shape and aportion of a full mirror length of the mirror shape as joined byflanges.

FIG. 12 illustrates, in plan view as seen from the back side of mirror,yet another embodiment of mirror construction via a sandwich structuredcomposite having multiple pre-formed mirror segments, each segmentimplementing a portion of a full mirror aperture of a mirror shape, anda portion of a full mirror length of the mirror shape as joined bycontinuous ribs.

FIG. 13a illustrates, in side elevation view looking down a trough of amirror lengthwise, an embodiment of a suspension mechanism of themirror, with the mirror suspension mechanism in a horizontal position.

FIG. 13b illustrates the elements of FIG. 13a , with the mirrorsuspension mechanism in a vertical position.

FIG. 13c illustrates, in front elevation view, an embodiment of thesuspension mechanism of FIGS. 13a and 13 b.

FIG. 14a illustrates, in perspective view, an embodiment of a bearingmechanism connecting a solar receiver to a solar concentrator and tobuilding superstructure.

FIG. 14b illustrates selected details of FIG. 14a , with elementsconnecting to the building superstructure omitted for clarity.

FIG. 14c illustrates FIG. 14b in exploded view.

FIG. 14d illustrates selected details of FIG. 14a , with elementsconnecting to the solar concentrator omitted for clarity.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures illustrating selecteddetails of the invention. The invention is described in connection withthe embodiments. The embodiments herein are understood to be merelyexemplary, the invention is expressly not limited to or by any or all ofthe embodiments herein, and the invention encompasses numerousalternatives, modifications, and equivalents. To avoid monotony in theexposition, a variety of word labels (including but not limited to:first, last, certain, various, further, other, particular, select, some,and notable) may be applied to separate sets of embodiments; as usedherein such labels are expressly not meant to convey quality, or anyform of preference or prejudice, but merely to conveniently distinguishamong the separate sets. The order of some operations of disclosedprocesses is alterable within the scope of the invention. Wherevermultiple embodiments serve to describe variations in process, method,and/or features, other embodiments are contemplated that in accordancewith a predetermined or a dynamically determined criterion performstatic and/or dynamic selection of one of a plurality of modes ofoperation corresponding respectively to a plurality of the multipleembodiments. Numerous specific details are set forth in the followingdescription to provide a thorough understanding of the invention. Thedetails are provided for the purpose of example and the invention may bepracticed according to the claims without some or all of the details.For the purpose of clarity, technical material that is known in thetechnical fields related to the invention has not been described indetail so that the invention is not unnecessarily obscured.

Introduction

This introduction is included only to facilitate the more rapidunderstanding of the Detailed Description; the invention is not limitedto the concepts presented in the introduction (including explicitexamples, if any), as the paragraphs of any introduction are necessarilyan abridged view of the entire subject and are not meant to be anexhaustive or restrictive description. For example, the introductionthat follows provides overview information limited by space andorganization to only certain embodiments. There are many otherembodiments, including those to which claims will ultimately be drawn,discussed throughout the balance of the specification.

In some circumstances, techniques described herein enable cost reductionof concentrated solar power systems. In various embodiments, collection(concentration and conversion of solar energy) is separated fromprotection. A protective transparent exoskeleton (such as a glasshouseor a greenhouse) surrounds and/or encloses collecting elements (oralternatively the collecting elements are placed in the exoskeleton),enabling the collecting elements (mirrors, lenses, etc) to be lessrobust than otherwise required. By separating collecting and protectingfunctions, and leveraging off-the-shelf technology (e.g. highlyengineered, cost effective, and proven greenhouse technology, such asglass growers greenhouse technology) for the protection function, insome circumstances a reduction in cost and complexity of a system (suchas mirrors/lenses, support structure, foundations, tracking mechanisms,etc.) is enabled with a relatively minimal impact on overallperformance. The glasshouse is relatively low to the ground with littlewind force bearing surfaces, and is designed to withstand wind andweather with a relatively minimal structural skeleton. Because theglasshouse reduces wind forces acting on the collector and receiverelements, the mirrors or lenses used for collection and concentrationinside the exoskeletal protection of the glasshouse are enabled to belightweight, in some embodiments, to a point of seeming flimsy, and thusare relatively less costly to construct, transport, support and aim, andhave little or no weatherization costs. Note that within thisdisclosure, the terms glasshouse and greenhouse are usedinterchangeably, and are not meant to necessarily imply any sort ofhorticultural activity.

The protected embodiment techniques enable reflectors built from lightermaterials with simpler and lighter frames since wind, weather, and UVlight are reduced inside a glasshouse enclosure. Foundation, suspension,and tracking mechanisms for receivers and concentrators are enabled tobe simpler, lighter, and less expensive.

Some embodiments of a concentrated solar system inside a glasshouse havean array of relatively large 2-D-freedomed, 1-D-solar-tracking parabolictroughs suspended from fixed roof locations.

According to various embodiments, concentrators are made entirely orpartially of thin-gauge aluminum foil, reflective film, or otherrelatively reflective and lightweight materials. Some of the materialshave higher reflectivity than glass mirrors. Concentrators, in someembodiments, are foam core combined with reflective material, enablingconcentrators weighing less than one kg per square meter. Lightweightconstruction, in some usage scenarios, reduces one or more of costsassociated with production, transportation, and installation ofconcentrators. Total weight for some enclosed concentrated solar energyembodiments (including exoskeleton and protected collector) is less than20 kg per square meter of concentrator.

The glasshouse structure is primarily fixed and immobile, and trackingsystems control and aim the less than one kg per square meterconcentrators inside the structure in an environment having relativelysmall wind forces.

Integration of Receiver and Greenhouse Structure

In some embodiments, a receiver and concentrator are suspended fromsuperstructure of an enclosing greenhouse, enabling use of substantialsupport infrastructure of structure of the greenhouse. Lightweightreceivers and troughs, hung from the greenhouse (e.g. roof structure,trusses, and/or end posts), are held in place and aimed with relativelysmall members that exert force mostly in tension, thus avoiding use ofrelatively larger members compared to structures held in place and movedwith members in compression and subject to bending. The receiver issuspended at a fixed position relative to the greenhouse and theconcentrator is suspended with its focal line held on the receiver butable to rotate around the receiver to track the daily and/or seasonalmotion of the sun.

Design of Hanger, Rotating Joint and Bearing

In some embodiments, a hanger with a rotating joint is held in placesuspended from roof superstructure of a greenhouse. A receiver tube isrigidly connected to the hanger, thus supporting the receiver tube. Therotating joint is connected to the hanger with a bearing enabling thejoint to rotate around the receiver tube. A trough is suspended from therotating joint. All the weight of the joint and the trough is carried bythe rotating joint, through a bearing and to the hanger and then up tothe roof superstructure. The rotating joint is enabled to rotate forsmall adjustments during the day, through about ½ turn from winter tosummer, and another ½ turn back from summer to winter. In some usagescenarios, during an entire lifetime of the joint, it rotates theequivalent of no more than 100 revolutions and never needs to rotatemore than about 1 rpm. The hearing and the rotating joint are designedto avoid shading the receiver tube and to withstand high temperatures(e.g. hundreds of degrees C.) since the bearing and the joint arenecessarily in close thermal proximity to a high temperature thermalmedium and the receiver tube.

Concentrated Solar Energy System

Industrial scale concentrated solar power systems, in some embodiments,cover multiple acres of land, with large-scale systems practical in thehundreds of acres. FIG. 1 illustrates a perspective view of selecteddetails of an embodiment of an enclosing greenhouse and an enclosedconcentrated solar energy system for a small portion of a system.Greenhouse 25 has low internal shading and low cost. According tovarious embodiments, the greenhouses are less than an acre to hundredsof acres in size. Suitable commercial greenhouses are available withshort lead times from various vendors. Additionally, in some usagescenarios, there is a market for used greenhouses, enabling relativelyeasier financing of large-scale concentrated solar energy projects, suchas described herein.

An optional dehumidification system reduces internal relative humidity,enabling, in some operating conditions, an extended usable lifetime ofreflector materials and/or control electronics. Condensation (e.g. thatoccurs on a daily basis in some seasons in some locations) causesbonding of dust to surfaces and leads to corrosion reactions. Airbornehumidity also accelerates corrosion reactions and performancedegradation in reflector materials, as is well-understood andwell-documented in lifecycle evaluations of reflector materials forconcentrating solar systems. The optional dehumidification system (used,e.g., for managing relative humidity) enables using less robust and lesshumidity-resistant reflective concentrator materials, resulting in costreductions and/or performance improvements, in some embodiments and/orusage scenarios.

In some embodiments, many troughs are enclosed in a single greenhousewith one front trough 27 and all the rest rear troughs such as 28. Insome embodiments, the troughs are aligned east/west, with troughs facingthe equator as illustrated, and track seasonal movement of the sun. Insome embodiments, the troughs are aligned north/south (not illustrated).

In FIG. 1, line-focus solar receivers are illustrated suspended fromreceiver pipes 12 that are in turn suspended from the roof of theenclosing greenhouse. Line-focus solar concentrators are suspended fromassociated solar receivers so that the focal point of the concentratoris held relatively fixed on the receiver while the concentrator bodyremains free to rotate around the receiver (in one degree of freedom) totrack daily and seasonal motions of the sun. The arrangement ofrelatively fixed receivers and concentrators that rotate around thereceivers to track the sun is enabled, at least in part, by low weightof the concentrators and absence of wind forces on the concentrators.

Various embodiments suspend receiver pipes 12 and pipes 8 from trusses 1or horizontal lattice girders. In some embodiments, solar receivers,such as implemented in part by receiver pipe 12, are interconnectedthrough a series of thermally insulated pipes (such as pipe 8). Theinsulated pipe connects the trough receiver pipe to a next troughreceiver pipe to complete a thermal fluid circuit.

Shape of Trough and Definitions of Terms and Formula

FIG. 2 illustrates a shape of a parabolic trough with an extension, suchas an embodiment of an asymmetric (parabolic) trough. The shape of theparabolic trough is defined by the formula y²=4 fx. With example valuesdescribed following, an example parabola is defined by the formulay²=5.8 x, where −2.29<x<4. A primary symmetric portion includes twosymmetric base trough sections 6 a and 6 b referred to and illustratedcollectively as base trough section 6, and also sometimes referred to as(symmetric) base portion (of the trough). A secondary extended portionincludes extended trough section 7, and is, in some embodiments, aunilateral extension of the parabolic shape. Bottom of trough 26 is theedge of the trough that is closest to the ground when the trough is heldvertical to face the sun low in the sky. Top of trough 30 is the edge ofthe trough that is furthest from the ground when the trough is heldvertical. In some embodiments, bottom of trough 26 is the edge ofextended trough section 7, and is further from the ground when thetrough is horizontal, pointed at the sun high in the sky (as illustratedin FIG. 2, given an orientation of the trough such that constructionline 34 is essentially horizontal to the ground). Trough focal length,illustrated by construction line 32 (e.g. having a value of 1.45meters), is represented by the symbol f. A symmetric trough has anaperture (referred to as a base aperture in a trough with an extension),defined by a construction line between its two edges, such asillustrated by construction line 34 across the symmetric portion andending at construction line 44, denoting intersection of the primary andthe secondary portions of the trough. Construction line 35 represents ahalf-portion of construction line 34 (e.g. having a value of 2.29meters). Construction line 33 indicates an extended aperture (e.g.having a value of 6.29 meters) of the asymmetric trough (referred tosimply as the aperture where clear from context), including base troughsection 6 and extended trough section 7. In some embodiments, extendedtrough section 7 is optionally movably connected to base trough section6, is optionally enabled to change shape and/or is optionally enabled tochange focus at an intersection defined by construction line 44.Construction line 48 defines an axis of symmetry of the symmetric baseportion of the trough and runs from the intersection of base troughsections 6 a and 6 b through focal point 36. Angles 37 a and 37 b arebase rim angles (sometimes referred to as the base rim angle forclarity) of the symmetric portion of the trough. Angle 38 is theextended rim angle of the extended portion.

Selected Details of a Movable Hinged Extension

FIG. 3 illustrates certain details of a parabolic trough with anextension, a receiver pipe, and an associated suspension mechanisms in acontext free of other details to make certain details easier tounderstand. Extension suspension member 5 is representative ofembodiments with fixed and/or movable extension suspension members, asappropriate. In the illustrated embodiment, the extension is hinged viahinged section connector 13, and has two sections fixedly connected viasection connector 15.

In some embodiments, construction and suspension of a trough isaccomplished by pinning together various elements, including suspensionmembers 4 and 5, base trough section 6, and extended trough section 7.Each segment of the concentrator is made from pre-formed mirror surfaceshaving sufficient internal structure to hold shape and curvature withoutuse of other elements, while under the force of gravity and small forcesimposed by suspension and positioning. The concentrators are enabled forinside use, protected by a greenhouse, and so are not strong enough towithstand wind force or environmental elements such as rain and dust.Suspension members are either light rigid members or wires. In eithercase, the suspension members connect to the concentrator surface, joint,hanger, or roof superstructure with pins that are readily insertable forassembly and readily removable for service.

Notes Regarding Selected Figures

Note that that in various embodiments, one or more of FIGS. 5a, 5b, 6a,6b, 6c, 7a, 7b, 7c, 8a, 8b, 8c , 9 a, 9 b, 9 c, 10, 11, 12, 13 a, 13 b,and 13 c, are not to scale. Note that in various embodiments, one ormore of FIGS. 5a, 6a, 7a, 8a, and 9a , are “conceptual” plan views forclarity of presentation, in that the respective illustration is as ifthe curvature present in the respective embodiment were not present.

Sandwich Structured Composite Solar Concentrators

In some embodiments and/or usage scenarios, enclosing solarconcentrators in a protecting structure enables the solar concentratorsto be less robust than otherwise, since the enclosed solar concentratorsare unaffected by environmental forces and/or hazards external to thestructure (such as wind, rain, dust, dirt, or hail). Solar concentratorsthat hold shape to a relatively high degree of accuracy over time andthroughout movement to aim at the sun enable efficient solar energycollection. In some embodiments and/or usage scenarios, deformation ofcollector/reflector shape causes reflected light to miss solar receiversand be wasted. In some situations, wind is the largest force acting onsolar concentrators located external to a protecting structure. In someembodiments and/or usage scenarios, gravity and forces applied to aimcollectors/reflectors are the largest forces acting on solarconcentrators located internal to a protecting structure.

In some embodiments, sufficiently stiff, lightweight, and inexpensivesolar concentrators are built of sandwich structured composites (see,e.g., http://en.wikipedia.org/wiki/Sandwich_structured_composite for anintroduction to sandwich structured composite materials) and do not needexternal support structure. Such frame-less mirrors are a monocoque(see, e.g., http://en.wikipedia.org/wiki/Monocoque for an introductionto monocoque structures) structure where the majority of structuralstress is carried in the skin of the structure.

FIG. 4 illustrates in exploded perspective view a section of a sandwichstructured composite with a honeycomb core. The sandwich structureincludes front skin 60, core 61, and rear skin 62.

FIGS. 5a and 5b illustrate, in plan and exploded section views, somefeatures of a sandwich structured composite used to form a parabolictrough solar concentrator. In various embodiments, front skin 63 thatforms the mirror surface of a solar concentrator is made from polishedaluminum sheet, back surface mirrored glass, or front surface mirroredglass. In various embodiments, core 64 (with the honeycomb illustratedmuch larger than scale) is made from aluminum honeycomb or foam sheet.In some embodiments, rear skin 65 is made from aluminum sheet or steel.Materials are selected of appropriate thickness to provide requiredstrength (e.g. stiffness) against relatively local deformation, (e.g.due to thermal expansion and/or manufacturing variations) as well asrelatively global lengthwise, widthwise, and/or twisting (torsional)deformation of the trough. For a solar concentrator of 7.5 metersaperture, 1.95 meters focal length and 17.5 meters length, a frontaluminum skin of 0.4 millimeters thickness with an aluminum honeycombcore of 40 millimeters thickness and a rear aluminum skin of 0.2millimeters thickness is suitable and is optionally supportable only at4 points (two on the edge of the trough, and two in the middle of thetrough) every 2.5 meters along the length of the trough by supportingrods and/or supporting cables from above. A solar concentrator builtwith these materials weighs, in some embodiments, less than 4 kilogramsper square meter. Materials are selected with appropriately matchedthermal expansion characteristics to avoid deformation stress as thesolar concentrators experience a range of temperatures that in someembodiments, extends from −20 degrees Celsius to 80 degrees Celsius. Insome embodiments, heat activated glue is used to bond the front skin,the core and the rear skin.

Enhanced Sandwich Structured Composite Solar Concentrators

In some embodiments, as illustrated in FIGS. 6a, 6b, and 6c , front skin67 is sufficiently strong such that portions of a concentrator areconstructed of a front skin alone with no sandwich in those areas. Insome embodiments, the front skin thickness is selected to providestiffness against local deformation without need for core or rear skin.Other portions of the concentrator use, in some embodiments, addedstrength provided by sandwich structure, such as illustrated by core 68(with the honeycomb illustrated much larger than scale) and rear skin69. In some embodiments, curvature of a concentrator trough ismaintained by sandwich structure portions widthwise from top to bottomof the trough at periodic intervals. In some embodiments, a shape of atrough along its length is maintained by sandwich structure portionsfrom edge to edge lengthwise. In some embodiments, such as illustratedin FIGS. 6a, 6b, and 6c , lengthwise and widthwise sandwich structureportions are formed from a single piece of material with portionsremoved (e.g. removed material 70 and 71).

In some embodiments, such as illustrated in FIGS. 7a, 7b, and 7c , frontskin 74 is backed by sandwich portions that are formed from strips ofcore 75 (with the honeycomb illustrated much larger than scale) and rearskin 76 portions that are placed widthwise as illustrated, and/orlengthwise (not illustrated). In some embodiments, solar concentratorsconstructed with enhanced sandwich structured composites with portionsof core or rear skin material removed are lighter and/or use lessmaterial than sandwich structures without material removed.

In some embodiments, thin (such as 10 mm) core material is enabled toresist some forces (such as local deformations) but thicker (such as 50mm) core material is enabled to resist other forces (such as lengthwiseand/or widthwise forces). In some embodiments, core material is selectedto satisfy the thickest core requirement. In some embodiments, such asillustrated in FIGS. 8a, 8b, 8c, 9a, 9b, and 9c , triple skin sandwichstructured composite construction is employed. In some embodiments, thinfront core 81/91 (such as 10 mm honeycomb) is used between front skin80/90 and middle skin 82/92. Thick (such as 50 mm honeycomb) rear core83/93 is used between middle skin 82/92 and rear skin 84/94, while rearcore 83/93 and rear skin 84/94 have selected portions removed 85 and 86,respectively (as illustrated in FIGS. 8a, 8b, and 8c ), or are ribbed(as illustrated in FIGS. 9a, 9b, and 9c ).

In some embodiments, (not illustrated) of a triple skin structuredcomposite, a rear core and a rear skin are constructed from multiplestrips of material used on portions of a concentrator. In someembodiments, a hybrid solar concentrator is constructed using a tripleskin structured composite (conceptually replacing selected areas of adouble skin structured composite of a first type). The hybrid solarconcentrator weighs less and/or uses less material than a solarconcentrator using a double skin structured composite (of the first typeor a second type) without using the triple skin structured composite. Invarious embodiments, solar concentrators constructed with enhancedsandwich structured composites weigh less than 3 kilograms per squaremeter.

Construction and Transportation of Solar Concentrators

Sandwich Structured Composite Solar Concentrators are, in someembodiments, pre-formed in a factory using a heated mold. In someembodiments of a construction process, front material is first placedover a lower mold having a desired curvature of a concentrator or aconcentrator section. In some embodiments, Front material is heldtemporarily in a proper shape next to the mold by vacuum applied throughholes in a face of the mold. Next glue is applied as a film, a spray orother application scheme. Next core material is applied. Next glue isagain applied. Finally rear skin material is placed over the core and atop mold is applied to place a concentrator sandwich formed from thepreviously assembled layers under pressure and heat to cure the glue. Insome embodiments with triple skin sandwich construction, additionallayers are applied either before the first glue is cured or in a latercuring step.

In some embodiments, a full trough is constructed in a single operation.In some embodiments, such as where trough size is too large to form on amold in a single piece, trough sections are constructed. In someembodiments, alignment holes or pins are added to troughs or troughsegments during construction to be used during trough mounting at adestination after transportation.

In some embodiments, a full trough is too large for practical shipmentto a destination. In some embodiments, a full trough or a trough sectionbuilt on a mold is cut, in place, into smaller sections for convenienceof transportation (e.g. shipping). In some embodiments where troughsections are cut, alignment holes or pins are added during manufacturingof the trough sections, the holes or pins for use in reconnecting thecut trough sections during trough mounting and/or assembly at adestination.

In some embodiments, such as illustrated in FIG. 10, a concentrator isconstructed of multiple segments, each forming an entirety of aparabolic curve of a trough concentrator (conceptually represented bywidthwise direction of trough and direction of trough curvature 101) anda portion of length (conceptually represented by lengthwise direction oftrough and direction of axis of symmetry 100) of the troughconcentrator. Each segment (illustrated, e.g., by one of multiple mirrorsegments 104) is connected to a next segment by flanges (illustrated,e.g. by one of multiple mirror connection flanges with integrated mirrorsuspension point 103) suspended from above at a fixed length from asolar receiver. A gap (illustrated, e.g., by widthwise gap betweenmirror segments 102) separates mirror segments lengthwise. In someembodiments, suspension rods or cables are pre-cut to an appropriatelength. In some embodiments, the rods or the cables have a facility forfine adjustment of length. In some embodiments, pre placed holes andpins on concentrator segments and flanges are used for alignment. Invarious embodiments, concentrator segments and flanges are joined byfasteners, rivets, or glue. In some embodiments, one or more seamsbetween trough segments are weak points. In some embodiments, segmentsof a trough are connected with sufficient strength to hold a shape ofthe trough. In various embodiments, additional trough suspension rods orcables are added at seams of a trough to hold the seams at a fixeddistance from a solar receiver. In some embodiments, tape is appliedacross a length of a seam to further strengthen the seam.

In various embodiments, such as illustrated in FIG. 11, a concentratoris constructed of multiple segments with seams in the lengthwisedirection (conceptually represented by lengthwise direction of troughand direction of axis of symmetry 110) and the widthwise direction(conceptually represented by widthwise direction of trough and directionof trough curvature 111). The segments are of various sizes and arrangedin an interstitial pattern to avoid long seams along a length of a solarconcentrator. The various sizes are illustrated, e.g., by one ofmultiple ‘small’ and ‘large’ mirror segments 114 and 116, respectively.Also illustrated are gaps between the mirror segments, as, e.g.,widthwise and lengthwise gaps between mirror segments 112 and 113,respectively. A flange is illustrated by, e.g., one of multiple mirrorconnection flanges with integrated mirror suspension point 115.

In some embodiments, such as illustrated in FIG. 12, a concentrator isconstructed with gaps in the lengthwise direction (conceptuallyrepresented by lengthwise direction of trough and direction of axis ofsymmetry 120) and seams in the widthwise direction (conceptuallyrepresented by widthwise direction of trough and direction of troughcurvature 121). Widthwise seams are connected between concentratorsegments with ribs (illustrated, e.g., by one of multiple mirrorsuspension ribs with multiple mirror suspension points 124) rather thanindividual flanges (such as illustrated in FIG. 11). Various mirrorsizes are illustrated, e.g., by one of multiple ‘small’ and ‘large’mirror segments 123 and 125, respectively. Also illustrated are gapsbetween the mirror segments, as, e.g., gap between mirror segments 122.In some embodiments, mirror suspension ribs are constructed as sandwichstructured composites. In some embodiments, mirror suspension ribs arepre-formed in a factory as connected to concentrator segments, withmirror suspension ribs extending beyond an edge of the concentratorsegment to provide a connection mechanism for a next concentratorsegment.

In some embodiments, such as illustrated in FIGS. 13a, 13b, and 13c ,ribs are suspended (e.g. from one or more solar receivers) duringconstructing within a glasshouse, enabling subsequent placement ofelements (e.g. of one or more concentrator segments) on top of andfastened to the ribs during the constructing.

Active Control of Twisting Forces

In some embodiments and/or usage scenarios, a curved structure (e.g. aparabolic trough) is relatively resistant to force lengthwise orthogonalto a radius of curvature, due at least in part to the curvature. In someembodiments and/or usage scenarios, a curved structure built from asandwich structured composite (e.g. a sandwich-composite-based parabolictrough) is relatively resistant to force along a radius of curvature, atleast in part due to the sandwich structure composite. In someembodiments and/or usage scenarios, a curved structure built from asandwich structured composite (e.g. a sandwich-composite-based parabolictrough) is, at least in part, further strengthened against the force ofgravity by suspension rods and/or suspension cables of a fixed lengthsuspended from a solar receiver. In some embodiments and/or usagescenarios, an “open” curved structure (e.g. a parabolic trough) is notrelatively resistant to torsion forces, due at least in part to thecurved structure being open rather than closed (e.g. a parabola insteadof a complete circle or ellipse).

In various embodiments, trough concentrators are stiffened againsttorsion force deformation via a torque tube or torque box running thelength of the concentrator (behind so as not to block incident light)and ribs extending from the torque tube or the box to the rear of theconcentrator. In various embodiments, the torque box or the torque tubeand the extending ribs add substantial weight and cost to theconcentrator.

FIGS. 13a, 13b, and 13c illustrate, in various views and positions, atrough embodiment. Illustrated are roof superstructure 130, receiversuspension cable/rod 131, mirror suspension cable/rod 134, mirrorsuspension rib 135, positioning cable 137, and positioning pulley 136.Further illustrated are solar receiver pipe 132 (the inner of the twoconcentric circles of FIG. 13a and FIG. 13c ) and pipe hanger/mirrorbearing 133 (the outer of the two concentric circles of FIG. 13a andFIG. 13c ).

In various embodiments, such as illustrated in FIGS. 13a, 13b, and 13c ,a concentrator is pulled by an edge at multiple points along the lengthof the concentrator to position the concentrator facing the sun.Multiple fixed length rods or cables suspend the concentrator at a fixeddistance (focal length) from a receiver. Multiple positioning rods orpositioning cables (either in line with the suspension rods or thesuspension cables or at separate points lengthwise along theconcentrator) are pulled to position the concentrator more verticallywhen the sun is low in the sky and eased to position the concentratormore horizontally when the sun is high in the sky.

In various embodiments, the suspension rods or the suspension cables andthe positioning rods or the positioning cables are all held almostexclusively in tension at all times. In some embodiments, thepositioning cable is mounted on the concentrator on one end and on aroof superstructure at an extended distance from directly above theconcentrator so that when the concentrator is raised the positioningcable pulls the concentrator to keep one or more of the suspensioncables or the suspension rods in tension. If the suspension members orthe positioning members were sometimes subject to compression, then thesuspension cables could not be used and the suspension rods would needto be substantially larger. In addition to adding cost and weight to asystem, the larger suspension rods would, in some embodiments, reduceefficiency by blocking additional incident light.

In some embodiments where concentrators are oriented lengthwise fromeast to west, positioning members (e.g. rods or cables) are only used onone side of the concentrators (as illustrated). In various embodimentswhere concentrators are oriented lengthwise from north to south, or someembodiments where concentrators are oriented lengthwise from east towest and having a center of gravity necessitating pulling at times fromone side and at times from the other to properly track the sun duringall daylight hours, positioning members are used on both sides of theconcentrators (not illustrated).

Where multiple positioning rods or positioning cables are placedlengthwise along a concentrator, torsional forces are reduced and/orminimized, in some embodiments, with no additional strengthening of theconcentrator against torsional distortion. In some embodiments, allpositioning rods or positioning cables on one side of a concentrator aremoved together by one motor or by multiple motors controlled together byone sensor system. In some embodiments, fine tuning of aiming isachieved by moving individual positioning cables under control ofseparate motors and using local sensors to determine optimal positionsof the individual positioning cables. In some embodiments where multiplemotors are controlled separately by respective positioning controlsystems, additional resilience is achieved against failure of any one ofthe motors or any one of the positioning control system because theother motors under control of their individual positioning controlsystems remain enabled to aim the concentrator.

Concentrator Suspension Mechanism Design Considerations

FIGS. 14a, 14b, 14c, and 14d illustrate, in various views, an embodimentof a bearing mechanism connecting a solar receiver to a solarconcentrator (not illustrated) and to building infrastructure (notillustrated). Illustrated and specifically identified in FIG. 14a aresolar receiver 140, solar concentrator suspension rod 141 (multipleinstances), and solar receiver suspension rod 142 (multiple instances).Illustrated and specifically identified in FIG. 14c are concentratorhanging top portion with bearing outer ring 143, split bearing raceway144, and concentrator hanger bearing strap 145. Illustrated andspecifically identified in FIG. 14d are receiver hanger 149. sixfasteners 146 connecting split bearing raceway 144 to receiver hanger149 and split ring tightening mechanism, and bolt 148 to attach solarreceiver hanger 149 to solar receiver 140 by closing ring to specifiedtorque. Also identified in FIG. 14d are solar receiver 140, solarreceiver suspension rod 142 (multiple instances), and split hearingraceway 144.

In some embodiments, a continuous solar receiver is a combination (e.g.connected in series and/or in parallel) of out (e.g. outlet) and back(e.g. inlet) pipes suspended from a roof of a greenhouse, attached atone end to a wall of the greenhouse and free to move at the other end.The suspension mechanism enables a continuous solar receiver to expandand contract as the continuous solar receiver heats and cools whilebeing held in straight lines by a suspension mechanism. A solarconcentrator is suspended from the continuous solar receiver with afocal line of the solar concentrator fixed on the solar receiver andwith the solar concentrator enabled to rotate around the continuoussolar receiver to track the sun. In some embodiments, a mechanism toconnect a solar receiver to a greenhouse roof and a solar concentratorto the solar receiver is built from a single joint clamped to the solarreceiver as illustrated in FIG. 14a . A clamping mechanism enablestightening of the joint mechanism to the solar receiver while allowingfor manufacturing variation in an outside diameter of the solarreceiver. Structure of the joint structure is illustrated with variouselements omitted in FIGS. 14b, 14c, and 14d . FIG. 14b omits elements ofFIG. 14a that connect to the building superstructure, and FIG. 14c is anexploded view of FIG. 14b . FIG. 14d omits elements of FIG. 14a thatconnect to the solar concentrator.

In some embodiments, light is reflected by a solar concentrator and isincident upon a joint mechanism. In some embodiments, joint mechanismwidth is minimized so as to block as little incident light as possible.In some embodiments, as illustrated in FIG. 14c , a concentratorsuspension mechanism is built with a thin strip of material forming anouter portion of a rotating bearing (operable as a concentrator hangerbearing strap) to minimize an amount of material between incident lightreflected by a solar concentrator and a solar receiver under a jointmechanism. The thinness of the concentrator hanger bearing strap isenabled by the concentrator bearing rotating only through part of a fullcircle and always maintaining a position such that weight on the solarconcentrator is supported by concentrator hanging top portion withbearing outer ring 143. The thin concentrator hanger bearing strapprovides a low resistance thermal path between a concentrator and aconcentrator hanger top portion. In some embodiments, a concentratorhanger bearing strap is coated with a selective coating the same as orsimilar to a selective coating applied to a solar receiver to maximizeabsorption of incident solar radiation and/or to minimize emission ofradiation from the solar receiver when heated. In some embodiments, aconcentrator hanger bearing strap is coated with a non-selective coatingto maximize absorption of incident solar radiation but to allow emissionof radiation from a concentrator hanger hearing strap in case a thermalpath between a concentrator hanger hearing strap and a solar receiver isinsufficient to maintain the concentrator hanger bearing strap below amaximum operating temperature.

Selected Embodiment Details

In various embodiments and/or usage scenarios, the illustratedembodiments are related to each other. For example, in some embodimentsand/or usage scenarios, mirrors, as depicted in FIGS. 5a, 5b, 6a, 6b,6c, 7a, 7b, 7c, 8a, 8b, 8c , 9 a, 9 b, and 9 c, are implementationtechniques for all or any portion(s) of solar concentrators (e.g. ofFIGS. 1, 13 a, and 13 b), reflective surface(s) of troughs (e.g. of FIG.2), and mirrors (e.g. of FIG. 3). For example, in some embodimentsand/or usage scenarios, positioning member 9 of FIG. 1 is an alternateembodiment of positioning cable 137 of FIGS. 13a and 13 b.

While the forgoing embodiments are described as having roof systems withpeaks and gutters, other embodiments use alternate roof systems, such aspeaked, arched, mansard, and Quonset-style roof systems, as well asvariations and combinations thereof. In various embodiments, a partiallytransparent protective enclosure (such as a glasshouse or a greenhouse)uses glass to provide the transparency, and other embodiments usealternative transparent materials such as plastic, polyethylene,fiberglass-reinforced plastic, acrylic, polycarbonate, or any othermaterial having suitable transparency to sunlight and sufficientstrength (in combination with a supporting framework) to provideenvironmental protection.

CONCLUSION

Certain choices have been made in the description merely for conveniencein preparing the text and drawings and unless there is an indication tothe contrary the choices should not be construed per se as conveyingadditional information regarding structure or operation of theembodiments described. Examples of the choices include: the particularorganization or assignment of the designations used for the figurenumbering and the particular organization or assignment of the elementidentifiers (the callouts or numerical designators, e.g.) used toidentify and reference the features and elements of the embodiments.

The words “includes” or “including” are specifically intended to beconstrued as abstractions describing logical sets of open-ended scopeand are not meant to convey physical containment unless explicitlyfollowed by the word “within.”

Although the foregoing embodiments have been described in some detailfor purposes of clarity of description and understanding, the inventionis not limited to the details provided. There are many embodiments ofthe invention. The disclosed embodiments are exemplary and notrestrictive.

It will be understood that many variations in construction, arrangement,and use are possible, consistent with the description, and are withinthe scope of the claims of the issued patent. The names given toelements are merely exemplary, and should not be construed as limitingthe concepts described. Also, unless specifically stated to thecontrary, value ranges specified, maximum and minimum values used, orother particular specifications, are merely those of the describedembodiments, are expected to track improvements and changes inimplementation technology, and should not be construed as limitations.

Functionally equivalent techniques known in the art are employableinstead of those described to implement various components, sub-systems,operations, functions, or portions thereof.

The embodiments have been described with detail and environmentalcontext well beyond that required for a minimal implementation of manyaspects of the embodiments described. Those of ordinary skill in the artwill recognize that some embodiments omit disclosed components orfeatures without altering the basic cooperation among the remainingelements. It is thus understood that much of the details disclosed arenot required to implement various aspects of the embodiments described.To the extent that the remaining elements are distinguishable from theprior art, components and features that are omitted are not limiting onthe concepts described herein.

All such variations in design are insubstantial changes over theteachings conveyed by the described embodiments. It is also understoodthat the embodiments described herein have broad applicability to otherapplications, and are not limited to the particular application orindustry of the described embodiments. The invention is thus to beconstrued as including all possible modifications and variationsencompassed within the scope of the claims of the issued patent.

What is claimed is:
 1. A system comprising: a front layer having outerand inner surfaces, the front layer being reflective to incident solarradiation; a honeycomb core layer; a rear layer having outer and innersurfaces; wherein at least a portion of the honeycomb core layer issituated between the inner surfaces of the front and the rear layers andis bonded directly to the inner surface of the front layer; wherein thefront, the rear, and the honeycomb core layers are laminated tocollectively have a weight of less than 4 kilograms per square meter,and operate as a line-focus solar energy concentrator of the incidentsolar radiation.
 2. The system of claim 1, wherein glue bonds the frontlayer, the honeycomb core layer, and the rear layer.
 3. The system ofclaim 2, wherein the front layer comprises polished aluminum sheet, thehoneycomb core layer comprises aluminum honeycomb, and the rear layercomprises aluminum sheet.
 4. The system of claim 2, wherein the frontlayer comprises polished aluminum sheet, the core honeycomb layercomprises an aluminum honeycomb layer that is continuous in a directiontransverse to a focal line of the solar energy concentrator, and therear layer comprises aluminum sheet.
 5. The system of claim 2, whereinthe front layer comprises mirrored glass sheet and the rear layercomprises steel sheet.
 6. The system of claim 2, wherein the front layercomprises one of polished aluminum sheet, back surface mirrored glass,and front surface mirrored glass.
 7. The system of claim 2, wherein across-section of the bonded layers approximates a segment of a paraboliccurve.
 8. The system of claim 2, further comprising one or more ribspositioned to support a section of the bonded layers via the outersurface of the rear layer.
 9. The system of claim 8, wherein the ribsare comprised of laminated composites.
 10. The system of claim 1 whereinthe front layer and the rear layer are each attached directly to thehoneycomb core layer.
 11. The system of claim 10 wherein at least one ofthe front layer and the rear layer includes a coating.
 12. The system ofclaim 11 wherein the front layer includes back surface mirrored glass.13. The system of claim 1 wherein the concentrator is positioned withina glass enclosure.
 14. The system of claim 13 wherein the concentratoris suspended from an overhead structural element of the glass enclosure.15. The system of claim 13, further comprising a dehumidification systempositioned within the glass enclosure.
 16. The system of claim 14,further comprising a plurality of independently controllable motorspositioned along a length of the concentrator to rotate theconcentrator.
 17. The system of claim 16, further comprising acontroller operatively coupled to the plurality of motors and programmedwith instructions that, when executed, direct the motors to move theconcentrator to track the sun.
 18. The system of claim 16 wherein afirst motor operates as a backup to a second motor.
 19. The system ofclaim 16, further comprising a plurality of sensors coupled tocorresponding motors.
 20. The system of claim 14 wherein theconcentrator is one of multiple concentrators, and wherein neighboringconcentrators are connected end-to-end in a longitudinal direction. 21.The system of claim 1, further comprising: a glass enclosure in whichthe concentrator is positioned; a dehumidification system positionedwithin the glass enclosure; a plurality of independently controllablemotors positioned along a length of the concentrator to rotate theconcentrator; and a controller operatively coupled to the plurality ofmotors and programmed with instructions that, when executed, direct themotors to rotate the concentrator to track the sun, wherein: theconcentrator is one of multiple concentrators, with neighboringconcentrators connected end-to-end in a longitudinal direction, and atleast one of the front layer and the rear layer includes a coating.